1. Field of the Invention
The present invention relates to flame retardants for polyamides. More particularly, it relates to flame retardants which do not cause damage for physical properties of polyamides nor blooming on a surface of a flame retardant molded product and flame retardant polyamide compositions having flame retardancy.
2. Description of Prior Arts
Highly flame retardancy of polyamide resins have been required depending upon developments of polyamide resins for usages in electric and electronic fields and construction fields, though the polyamide itself has self-extinguishing characteristic.
Typical flame retardants for imparting highly flame retardancy to polyamide resins include halide compounds, phosphorus compounds, metal hydroxides and metal oxides. Among them, the halide compounds and antimony trioxide have been usually used as typical flame retardants.
However, it is necessary to incorporate 20 to 50% by weight of the conventional flame retardants to the polyamide resin. As the result, the physical properties of the polyamide itself are damaged and the moldability of the composition is inferior and the incorporation of the conventional flame retardant is not economical.
The organic halides themselves do not have safety or generate toxic gases in their decompositions thereof. Thus, an environmental pollution may be caused, if a large amount of said organic halide is incorporated.
Recently, nitrogen type compounds have been studied as flame retardants for polyamides. Melamine and melamine derivatives, cyanuric acid, isocyanuric acid and derivatives thereof are typical flame retardants as described in the prior arts:
U.S. Pat. No. 3,660,344 and U.S. Pat. No. 3,663,495 disclose uses of melamine and derivatives thereof, U.S. Pat. No. 3,980,616 and British Pat. No. 1,484,151 disclose uses of cyanuric acid and isocyanuric acid and U.S. Pat. No. 4,001,177 discloses use of combination of melamine or a derivative thereof and cyanuric acid or isocyanuric acid.
Flame retardancy can be given by an addition of a small amount of each of these conventional flame retardants. However, they cause blooming on a surface of a molded product whereby white powder is formed on the surface to deteriorate appearance. Sometimes, a metal contacted with the surface is corroded or a desired hue can not be given disadvantageously.